goke: add GK7205V510 PTZ (GPIO pan/tilt stepper) support + gpiostep-openipc

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What

Adds PTZ (pan/tilt) support for Goke GK7205V510 cameras such as the NC-IPTC2200_DL, whose pan/tilt is driven by two 4-wire GPIO stepper coils (no Pelco/serial/I²C motor IC). The SoC is firmware-compatible with the existing gk7205v500 family (same kernel 4.9.37, osdrv, toolchain), so this ships a thin gk7205v510_lite alias defconfig plus two motor-driver options that share one pin map.

Pin map (taken from the vendor /proc/devcfg motor block):

• pan (roll) = GPIO 3, 4, 72, 73
• tilt (pitch) = GPIO 69, 59, 58, 57

Two driver tracks (share the pin map)

Track A — userspace gpio-motors (sysfs bit-bang, already proven on GK7205V200)

• Enables BR2_PACKAGE_GPIO_MOTORS on gk7205v500_lite / gk7205v510_lite.
• Documents the device in gpio-motors/Readme.md: fw_setenv gpio_motors '3 4 72 73 69 59 58 57'.

Track B — new gpiostep-openipc package

• In-kernel GPIO half-step stepper driver: misc char dev /dev/motorDev + a single GPIOSTEP_MOVE ioctl, plus a gpiostep-ctl CLI.
• Same 8-phase half-step sequence as gpio-motors, but driven from kernel context (gpio_set_value + usleep_range) for steadier timing and lower CPU.
• Pins default to the GK7205V510 layout and are overridable via module params (insmod gpiostep.ko pan_gpios=... tilt_gpios=...).
• CLI mirrors gpio-motors' <pan> <tilt> <delay_ms> signature, so the two implementations can be A/B compared 1:1.

Changes

• br-ext-chip-goke/configs/gk7205v510_lite_defconfig (new, alias of v500; SOC_MODEL=gk7205v510, SOC_FAMILY=gk7205v500)
• br-ext-chip-goke/configs/gk7205v500_lite_defconfig (+GPIO_MOTORS, +GPIOSTEP_OPENIPC)
• general/package/gpiostep-openipc/ (new package: Config.in, .mk, src/{gpiostep.c,gpiostep.h,gpiostep-ctl.c,Kbuild}, Readme)
• general/package/gpio-motors/Readme.md (GK7205V510 device entry)
• general/package/Config.in (register new package)

Testing

• make BOARD=gk7205v500_lite and make BOARD=gk7205v510_lite build clean (exit 0).
• Fits 8 MB NOR: uImage 1852/2048 KB, rootfs.squashfs 4460/5120 KB.
• gpiostep.ko links against the goke 4.9.37 kernel (only benign -Wmissing-attributes).
• Static gpio-motors / gpiostep-ctl (goke toolchain) confirmed to run on real GK7205V510 hardware.
• Not yet done: on-gimbal motion + phase-order confirmation (needs physical observation; the [0,2,1,3] coil-order fallback is documented in both Readmes).

🤖 Generated with Claude Code

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Hardware bring-up note (from probing a real GK7205V510 / NC-IPTC2200_DL)

The pan/tilt pin map is confirmed from the vendor /proc/devcfg motor block:

• tilt (pitch) = GPIO 69,59,58,57
• pan (roll) = GPIO 3,4,72,73

The pan coil needs a GPIO bank that is currently disabled. GPIO 72/73 live in group 9 (gpio_chip9@120b9000, base 72). In the openipc/linux goke DTSI (xm72050300.dtsi) gpio_chip9 is status = "disabled", and the board DTS xm72050500-demb.dts only enables chips 0,1,2,4,5,6,7,8. The vendor kernel is the same — it reaches 72/73 by ioremapping 0x120b9000 directly inside its gpioStep module, bypassing gpiolib.

So for the pan axis to work via either driver (sysfs gpio-motors or the new gpiostep module, both of which use gpiolib), the board DTS needs:

&gpio_chip9 { status = "okay"; };   // base 72, pan coil GPIO 72/73

The tilt axis (GPIO 69,59,58,57 → chips 7/8, already enabled) works as-is.

This is a kernel/DT change (openipc/linux), tracked separately from this packaging PR. On-gimbal motion + phase-order tuning to be done on OpenIPC hardware (Phase 2) — bit-banging on the live vendor firmware is not viable (it races the vendor motor stack's HW step timers and trips the 60s hardware watchdog).